GB647950A - Improvements in or relating to electrical pulse generating circuits - Google Patents

Abstract

647,950. Television. ELECTRIC & MUSICAL INDUSTRIES, Ltd. June 4, 1947, No. 14746. [Class 40 (iii)] [Also in Group XL (c)] A pulse generator comprises a number of valve stages arranged in cascade each having a stable and unstable state so that when one of the stages is changed to its unstable state it remains there for a predetermined period determined by a time constant circuit and on reversion causes the next stage to change to its unstable state the changes in the state of the stages thus generating pulses of predetermined durations. Fig. 1 shows a generator comprising valves 1 and 2 connected as a trigger pair and valves 12-15 connected with their grid leaks returned to H.T.+ so that they are normally conducting. When a positive pulse is applied to input 45 the trigger pair changes over with valve 1 conducting and 2 cut-off, the negative pulse at anode 5 cuts-off valve 12 which remains cut-off for a period adjustable by the value of the time constant of network 10, 11. On reversion to its stable conductive state the negative pulse at anode 20 is applied to cut-off the next valve 13. The sequence thus passes down the chain until the positive pulse at the cathode of valve 15 restores the trigger pair to its initial condition with valve 2 conducting. The voltages produced across the cathode resistors 38-40 constitute a succession of negative pulses of duration determined by the time-constants of networks 10, 11 ; 28, 29 ; 30, 31. The generator may be used in a time-multiplex system the pulses being used to gate signals from a number of subsidiary channels to apply them sequentially to a main channel. The generator may be used in a television system in which it is required to send a number of signals to a camera over a single channel from a central control point. Fig. 4 shows in schematic form such a television system. The line synchronizing signals 80 are applied to a gating pulse generator 85, as shown in Fig. 1, and the gating signals are used to pass pulses sequentially from cue-lamp signal sources 82, 83 and from a speech source 81 the speech and line synchronizing signals being applied to modulator 86 to give a line synchronizing signal which is width modulated by the speech channel. The gated signals are applied together with the frame synchronizing signals from source 84 to the line or camera cable 88 via the mixer 87. At the camera position the line synchronizing signals are separated by unit 92 and are used both to synchronize the camera 89 and to trigger the gating pulse generator 90 which is of the type shown in Fig. 1. The gating signals from unit 90 are applied to the separator 91, shown in Fig. 3. The negative pulses from the cathodes of valves 12-14, Fig. 1, are applied to diodes 61 to 63 to render them conductive for the duration of the applied pulses thus operating the telephones 68 or cue-lamp relays 69, 70 in the anode circuits of the associated amplifiers 65-67. A positive pulse derived from the anode of valve 15, Fig. 1, is applied to open gating valve 71 thus letting through the frame synchronizing signal from the input 46. In an interlaced television system in which the frame synchronizing signals occupy different positions at the end of odd and even frames respectively, the frame gating signal is made of sufficient duration to select frame pulses occupying either of such positions the pulses from the subsidiary channels occurring within the shorter interval or after the longer interval at which a frame synchronizing pulse follows a line synchronizing pulse, Fig. 2 (not shown). Reference has been directed by the Comptroller to Specification 614,220, [Group XL (c)].